Imaging

Myositis

Preliminary Diagnosis: Myositis

I. What imaging technique is first-line for this diagnosis?

  • MRI without gadolinium

II. Describe the advantages and disadvantages of this technique for diagnosis of myositis.

Advantages

  • May be diagnostic in the correct clinical scenario

  • Can detect the sequela of long-standing disease: fatty muscular replacement, muscular atrophy, and fascial thickening

  • Can detect the early changes of disease (ie, edema) prior to the development of calcification

  • Whole body MR imaging may detect other sites of involvement, which may not be clinically evident

  • Can accurately diagnose complications associated with steroid treatment: avascular necrosis and insufficiency fractures

  • Can detect other causes of muscle pain and weakness: ie, contusions, infection, and radiation-induced myositis

  • Does not make use of any ionizing radiation

  • Preferred imaging modality for selecting muscles to biopsy when a histopathologic diagnosis is required

Disadvantages

  • Expensive

  • Time consuming

  • Requires significant patient cooperation to minimize motion artifact

  • Less reliable for detecting osteopenia, a complication of steroid therapy

III. What are the contraindications for the first-line imaging technique?

  • Contraindicated in patients with non–MR-compatible metallic hardware or foreign bodies

IV. What alternative imaging techniques are available?

  • Non-enhanced CT

  • Plain film radiography

V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of myositis.

Non-enhanced CT

Advantages

  • May quickly and accurately identify the amorphous, punctate, or sheet-like calcifications that may develop over time

  • More reliable in demonstrating the distribution of calcium than MRI

  • Very sensitive in detecting osteopenia, a complication of steroid therapy

  • May be performed much more quickly than MR imaging, requires less patient cooperation, and is associated with less motion artifact compared with MR imaging.

Disadvantages

  • Exposes the patient to a large amount of ionizing radiation

  • Lacks the anatomical detail afforded by MRI

  • Much less sensitive compared with MRI in detecting intramuscular, perimuscular, or subcutaneous edema

Plain film radiography

Advantages

  • Can quickly identify subcutaneous, muscular, and fascial calcifications; osteoporosis; and muscular atrophy in a cost-effective manner

Disadvantages

  • Very nonspecific

  • Limited to detection of calcification in the setting of long-standing disease

  • Insensitive for detecting intramuscular, subcutaneous, and perimuscular edema

  • Utilizes ionizing radiation

VI. What are the contraindications for the alternative imaging techniques?

Non-enhanced CT

  • Contraindicated in pregnant women

Plain radiographs

  • No significant contraindications. Some institutions may require pregnant patients to sign a consent

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